Graded index (GRIN) glasses have been used for specific optical applications, e.g. GRIN lenses for fiber optics, for decades. Additionally, GRIN materials have been shown to provide advantages in more general lens designs. Unfortunately, actual utilization of GRIN materials has been limited to niche applications. This is due to limitations in the available index-of-refraction ranges and the cumbersome manufacturing required.
Since the introduction of gradient index optics in late 1960s there have been many attempts to improve the method of production or the materials used to create such optics. Methods including neutron irradiation, chemical vapor deposition, polymerization techniques, ion exchange, and crystal growth have all been explored. See D. T. Moore, Applied Optics 19, 1035 (1980). Photolithography has been used to induce gradient index lenses. See O. Doyle and T. Galstian, Optics Express 17, 4970 (2009). More recently, nanosized layered structures of two different types of polymers have been used to create graded-index lenses. See M. Sandrock et al., Applied Physics Letters 84, 3621 (2004); and A. R. Kamdar et al., Annual Technical Conference—Society of Plastics Engineers 65, 1743 (2007). However, In all cases the differences in index are relatively low and manufacturing of made-to-order lenses with the current material sets is very expensive.
Therefore, a need remains for a simple method to pattern a polymer to create a gradient index.